Heating on low all day- experiment

[User129867588]

Not sure anyone will find this useful as I know we all have different houses and boilers etc, but I trialled having my heating on all day yesterday, reduced my thermostat to 18 degrees and I spent the same on gas as previous day when the heating was on 18.5 but only on for just over an hour in morning and then for 3 hours in evening! Both days the temp on my thermostat after boiler being off all night was 14.5 degrees 🥶

House is a 2 bed semi, mid 1980’s build. Double glazing that’s over 10 years old and some getting replaced soon. House had insulation added but again that was about 15 years ago.

As seen on pictures the main expense on the gas was when heating first came on and then around tea time. I cooked on my gas hob and then all 3 of us had showers and we use a mixer shower connected to boiler for hot water. I’m with EDF on the variable rate.

I’m doing it again today and if it stays around the same I don’t see any reason for me to work in a cold house in the daytime when it costs the same (or just a tiny bit more) to heat most of the day! I can manage with 18 degrees too and still wear a jumper and extra thermals. Last years 20 degree heat is but a distant memory…….

That's not true for modern boilers. They can modulate their output to match demand. If you warm the house to x°C it wil run at full blast. Once it has achieved the desired temperature, it will maintain x°C by gently firing and your radiators will get barely warm.

I tried setting my flow temperature to 55°C. It didn't seem to work very well. The boiler, for reasons unknown, kept cutting out before the 55°C temperature was reached, which was also before the target room temperature was reached. I suspect the boiler may have been measuring the return temperature and shutting down if that exceeded the expected temperature, but that's very much a guess.

The boiler was set to 'automatic' partial load (Vaillant), which seems to be a known issue unless you're also using a Vaillant thermostat (ours is Honeywell).

I've changed the partial load to 18kW and the flow is currently set to 60°C.

I've ordered a laser thermometer from Amazon (£20) and I'm planning to properly balance the radiators via the TRVs instead of the lockshield valves. Once that has been completed, I will try a flow temperature of 55°C again.

I suspect that the boiler and thermostat might be fighting each other. It probably needs a smart controller that can constantly vary the flow temperatures and boiler output to get the best out of the system, but that might cost £500+ once we factor in the gas engineer.

One thing to remember with TRVs is that the radiator, in the same room as the thermostat, should be set to maximum. If you set the TRV to a room temperature lower than the thermostat, the room will never get warm enough for the thermostat to turn off your heating.

For example, you set the TRV to just under '3' (around 18°C), but the thermostat is set to 21°C, the temperature will never get warm enough to stop the boiler because the radiator in that room will be cold.

We haven't got a thermostat.

@NoWordForFluffy

www.askjeff.co.uk/need-heating-thermostat-will-trvs-job/

You might end up wasting money if all the rooms are up to temperature, so the radiators turn off, but the boiler is still burning.

It doesn't. The boiler goes off.

Plus we rent, so can't change anything.

Still on all 12 hours a day at 17.5 from 6:00 until 18:00 . I thought today would have been a lot more as I heard the heading click on more during the day but only 55p more since yesterday and we used the gas hob to cook today (went out for dinner yesterday so wasn’t used)
it barely got above zero today- 🥶

I tried this on Monday when I saw the thread - my gas for the day was £22 instead of £7! Shit!

It makes no logical sense for it to be anything other than more expensive. The only way the cost can be about the same is if the house is super insulated and doesn’t lose any heat once it’s warmed. Most houses aren’t super insulated.

My work colleague had a heating engineer around last week who told her it was more economical to do exactly this.

The point is that modern condensing gas boiler efficiency isn't fixed, but increases when you're not running it at full blast a few times a day and instead have it ticking over gently at a lower temperature. I was extremely sceptical, but the number of people finding that they can be more comfortable for only a little bit more money has convinced me to give it a try when my cavity wall and loft insulation is installed next week.

@Ciri

If you allow an object to cool, it requires exactly the same amount of energy to warm it up again. The net benefit from cooling then heating is zero.

The only difference is the thermodynamic aspect - a warmer object loses more heat than a cooler object.

If you keep your house at 18°C it will be losing more heat than when it's cooled to 14°C.

Is that saving worth it?

Our house isn't very well insulated.

1930’s with solid walls (no insulation)
10cm of loft insulation under the boards you walk on.
Double glazing - half modern, half 30+ years old.
Draft excluders in chimneys.

We do have a modern boiler and radiators (2019).

I think a modern central heating system, configured correctly (e.g. flow temperature of 60°C), in a double glazed home with minimal loft insulation, can be just as cheap to heat 24x7 as it is to heat twice a day. In fact, from what I can tell, it is cheaper to heat to 18°C 24x7, than heating to 21°C twice a day.

If you're in a house that cools so quickly, that it reaches ambient temperature between heating cycles, then it probably won't work. But I'd expect it to take weeks to truly reach ambient unless you're living in a tent. .

@Ciri I’m just as surprised as you! My house did have cavity insulation many years ago and to me to doesn’t seem like the warmest house . I do have a 5 year old A rated eco combi boiler so maybe that plays a part too. The thermostat also gauges what is required by the outside temperature

I don't think many (any?) who've done the experiment have found it's cheaper to keep it on all day. Just that it's it's not very much extra per day, and the delta might be worth paying for a much more comfortable house.

Of course it depends what your 'before' and 'after' temps were, but generally people who are finding the difference small have turned it down a few degrees.

The weather is way colder now than it was when OP started the thread, so it would be interesting to see what differences people are getting now.

We have a 1930s solid wall semi, we had the 30 year old double glazing replaced in the last 2 years and it has made quite a difference, we now have ice on outside of window. Earlier this year we decorated 2 bedrooms and put internal insulation on the external walls (Walkrock thermal liner), that has been effective, walls are no longer cold to the touch. The government has a new Eco grant scheme and my sister has just had cavity wall insulation, lift insulation done under the scheme, just waiting for date for a new boiler.

I agree.

One thing to bear in mind is flow temperature when maintaining the temperature. The small intermittent heating cycles don't result in the return temperature exceeding the condensation temperature, so the boiler will work more efficiently. If you allow the house to cool, and the heating needs to go on full whack, an incorrectly configured boiler (e.g. flow temperature of 70°C+ will result in a return temperature too high to condense and the boiler efficiency will drop (as much as 10%).

Now, if it only uses 7% more energy to maintain 18°C, vs intermittent heating, but the boiler is 10% more efficient, you can see cheaper bills. If it takes 13% more energy to maintain a temperature, you'd see higher bills.

For our family, I'm happy to go with 24x7 heating. My eldest son has asthma, we have a baby, DH works from home and I'm in the house pretty much all day.

Typical isn’t it. We’ve had some fairly mild winters recently. But it’s inevitable that we’re going to have a cold winter this year, with the war in Ukraine, and energy bills going up.

I just knew we’d be punished with a bad winter ahead.

Yeah, last winter was really mild and spring seemed to come early. It was freezing today and looks colder again tomorrow. Our heating was on for 6.5hrs yesterday and for a similar amount today, so tomorrow is going to be more again, I suppose.

I think if we had even a slightly lower target - we are at 19.5c - it would make a huge difference but I have crappy lungs and already had pneumonia once this year, so I'm not touching the thermostat.

Mine was on for 5 hours today to maintain 18.5 degrees all day, and off completely after 4pm.

That’s a lot of heating for quite a cool temperature.
1890s terrace

Todays central heating

Ours is also cheaper on 24/7 than set times.

£12.50 a day to keep a constant temperature. £14 if we have to reheat.

Have you checked your flow rate? Could try turning it up. Too high and you use more gas heating to an unnecessary higher temp. Too low and it won’t heat so the boiler is on continuously working overtime.

I would also check your radiators. Ours are boiling on top and cool at the bottom and need a powerflush as we must have a sludge issue.

@LemonSwan my flow rate is nearly max to get more heat round, but some radiators aren’t that hot and the boiler is over 10 yrs old

When you say 24/7 do you mean you keep your target temp at say 18.5 degrees day and night?